Function of Tyrosine Z in Water Oxidation by Photosystem II:  Electrostatical Promotor Instead of Hydrogen Abstractor

Ahlbrink, Ralf; Haumann, Michael; Cherepanov, Dmitry A.; Bögershausen, Oliver; Mulkidjanian, Armen Y.; Junge, Wolfgang

doi:10.1021/bi9719152

Cited by 193 publications

(309 citation statements)

References 101 publications

Supporting

Mentioning

266

Contrasting

Unclassified

Order By: Relevance

“…Such an increase is plausible in view of a more open structure of PSII after removal of the Mn cluster. At pH 5.7 electrochromism was practically absent (Figure 2, blue, dashed line) in agreement with our earlier data (37) and only a small chemical contribution from Y Z ox itself remained around 400 nm (58).…”

Section: Raw Absorption Difference Spectra and Their Deconvolutionsupporting

confidence: 92%

“…After this treatment oxygen evolution under continuous illumination (not documented) was below 10% of a control. The pH 9 treated samples were indistinguishable from samples that were inactivated by the classical tris-wash treatment (42,118) as apparent from transients of the reduction of P 680 + at 820 nm (37). Accordingly, it was likely that they were depleted of manganese (37,(42)(43)(44).…”

Section: Oxygenmentioning

confidence: 96%

“…To remove the contribution of Q A / Q A -from our UV spectra we normalized its difference spectrum (taken from Dekker et al (49)) to the observed UV extents at around 325 nm ( Figure 1, UV, dotted lines) and subtracted it from the former. The resulting differences from active centers and from inactive ones at pH 5.7 were scaled by factors of 1.2 to account for the amount of centers where Y Z ox has decayed after 20 µs in the former case and for a proportion of about 20% of total P 680 which stayed oxidized, P 680 + , in equilibrium with Y Z ox (37). To correct for the spectral contribution of P 680 f P 680 + , we furthermore subtracted 20% of its difference spectrum as taken from Gerken et al (50) from the data points at pH 5.7.…”

Section: Raw Absorption Difference Spectra and Their Deconvolutionmentioning

confidence: 99%

“…It is probably attributable to the pheophytin of branch A (15,47). We calibrated the contributions of Q A -to the spectra in the blue region on the basis of the electrochromic band shifts in the green ( -was reoxidized with a half-time of about 10 ms (52), and a small fraction of P 680 + was reduced in milliseconds (37). With Mn-depleted material the extents at 1 ms after a flash (repetition rate 0.1 Hz) were recorded with 200 µM DCBQ and 1 mM hexacyanoferrate(III).…”

Section: Raw Absorption Difference Spectra and Their Deconvolutionmentioning

confidence: 99%

“…However, the rate of the Y Z oxidation by P 680 + is fast (tens of nanoseconds) (115,116), almost insensitive to H/D substitution (33,(35)(36)(37), and has a low activation barrier (37,38), as characteristic for a pure electron-transfer event. Furthermore, the formation of Y Z ox is accompanied by a large and rapid electrochromic band shift of nearby pigments (15,34,39,40).…”

mentioning

confidence: 99%

See 4 more Smart Citations

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

1998

Self Cite

View full text Add to dashboard Cite

In oxygen-evolving photosystem II (PSII), a tyrosine residue, D1Tyr161 (Y Z ), serves as the intermediate electron carrier between the catalytic Mn cluster and the photochemically active chlorophyll moiety P 680 . A more direct catalytic role of Y Z , as a hydrogen abstractor from bound water, has been postulated. That Y Z ox appears as a neutral (i.e. deprotonated) radical, Y Z • , in EPR studies is compatible with this notion. Data based on electrochromic absorption transients, however, are conflicting because they indicate that the phenolic proton remains on or near to Y Z ox . In Mn-depleted PSII the electron transfer between Y Z and P 680 + can be almost as fast as in oxygen-evolving material, however, only at alkaline pH. With an apparent pK of about 7 the fast reaction is suppressed and converted into an about 100-fold slower one which dominates at acid pH. In the present work we investigated the optical difference spectra attributable to the transition Y Z f Y Z ox as function of the pH. We scanned the UV and VIS range and used Mn-depleted PSII core particles and also oxygen-evolving ones. Comparing these spectra with published in vitro and in vivo spectra of phenolic compounds, we arrived at the following conclusions: In oxygen-evolving PSII Y Z resembles a hydrogen-bonded tyrosinate, Y Z (-) ‚‚‚H (+) ‚B. The phenolic proton is shifted toward a base B already in the reduced state and even more so in the oxidized state. The retention of the phenolic proton in a hydrogen-bonded network gives rise to a positive net charge in the immediate vicinity of the neutral radical Y Z • . It may be favorable both for the very rapid reduction by Y Z of P 680 + and for electron (not hydrogen) abstraction by Y Z • from the Mn-water cluster.Photosystem II (PSII) 1 produces molecular oxygen from water. It is located in photosynthetic membranes of plants and cyanobacteria. The inner core of PSII is a heterodimer of the D1D2 subunits which show homology with the L and M subunits of the purple bacterial RC (1). The primary electron donor of PSII, P 680 , is located close to the lumenal side of the membrane. The absorption of a quantum of light drives the charge separation between P 680 and the quinone acceptor at the stromal side (2). The very high redox potential of P 680 + drives water oxidation. It is a four-stepped process with at least four increasingly oxidized, metastable states S 0 to S 3 , plus a transient state S 4 that decays in milliseconds into S 0 under release of O 2 . P 680 + is reduced (in nanoseconds) by a redox-active tyrosine residue, Y Z (D1Tyr161 (3, 4)). Y Z ox is, in turn, reduced in microseconds by the oxygenevolving complex (OEC). The structure and exact location of the OEC is still ill-defined. It is formed by four manganese atoms (5, 6), possibly another redox cofactor, X (7-9), plus at least one Cl -ion (10) and one Ca 2+ (11, 12) ion. These cofactors serve various functions during water oxidation: The Mn cluster stores at least two of the oxidizing equivalents (namely on transitions S ...

show abstract

Section: Raw Absorption Difference Spectra and Their Deconvolutionsupporting

confidence: 92%

Section: Oxygenmentioning

confidence: 96%

Section: Raw Absorption Difference Spectra and Their Deconvolutionmentioning

confidence: 99%

Section: Raw Absorption Difference Spectra and Their Deconvolutionmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

1998

Self Cite

View full text Add to dashboard Cite

show abstract

Photosynthesis, Artificial: Progress in Swedish Consortium

Ott

Styring

Hammarström

et al. 2005

Encyclopedia of Inorganic Chemistry

View full text Add to dashboard Cite

Mimicking energy conversion processes in nature using molecular systems is a promising approach for future solar fuel production. The Swedish Consortium for Artificial Photosynthesis is involved in the design, preparation and functional study of many of the key components needed for a homogeneous approach to artificial photosynthesis, building on principles from photosystem II (PSII) and [FeFe] hydrogenases. Ruthenium(II) polypyridyl complexes have played an important role as photosensitizers. Several strategies have been developed for their preparation, and a novel approach to improve the photophysical properties of bistridentate complexes involving six‐membered chelates for more octahedral coordination was recently introduced. The [Ru(dqp) 2 ] 2+ complexes (dqp is 2,6‐di(quinolin‐8‐yl)pyridine) combine the desired structural properties for easy access to linear donor–acceptor assemblies, while maintaining microsecond luminescent lifetimes of their 3 MLCT (metal‐to‐ligand charge transfer) excited states. The synthesis of these chromophores is now well established, and the recent realization of donor–photosensitizer–acceptor assemblies shows that photoproduced charge‐separated states can be formed in high yields (ϕ ≥ 95%). Beyond such single‐photon/single‐electron events, charge accumulation at potential catalytic sites is crucial for multielectron redox reactions. Covalently linked Ru II Mn x ( x = 1,2) complexes as PSII mimics have been investigated to understand chromophore–quencher (Mn quenchers) interactions, to promote desired electron transfer processes, and suppress undesired competing reactions. The Mn units often have large inner reorganization energies upon oxidation or reduction, which make them unusually slow electron donors and/or acceptors in photoinduced charge‐separation schemes. Charge accumulation and water splitting, however, require the management of both protons and electrons, which controls the electron transfer processes by proton‐coupled electron transfer (PCET). Studies on Ru II Tyr complexes incorporating pendant bases led to an understanding of the effect of hydrogen‐bonding on electron transfer rates. In analogy to the electron donor side, bioinorganic models of the [FeFe] H 2 ase active site are targeted for the electron acceptor side, with the ultimate goal to realize molecular catalysts that produce H 2 at similar high rates and low overpotential as the enzymes. Certain ligand sets create basic sites around the Fe centers that are protonated in the presence of acid and are thus models of late intermediates in the enzymatic catalytic cycle. Furthermore, synthetic Fe 2 complexes catalyze the electrochemical reduction of protons. In combination with a photosensitizer, they can also be used in photochemical schemes and are currently used to produce H 2 photochemically, with turnover rates up to 200.

show abstract

Role of Hydrogen Bonds in Photosynthetic Water Splitting

Ренгер¹

2010

Hydrogen Bonding and Transfer in the Excited State

View full text Add to dashboard Cite

Function of Tyrosine Z in Water Oxidation by Photosystem II: Electrostatical Promotor Instead of Hydrogen Abstractor

Cited by 193 publications

References 101 publications

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

Photosynthesis, Artificial: Progress in Swedish Consortium

Role of Hydrogen Bonds in Photosynthetic Water Splitting

Contact Info

Product

Resources

About